The development and growth of the wireless communication industry has made wireless communication environments in which various wireless communication technologies coexist. Wireless communication technologies, which have been commercialized, or which are expected to be commercialized in the near future, such as wireless communication standards, may include 2nd-Generation (2G), 3rd-Generation (3G) and 4th-Generation (4G) communication technologies. The 2G communication technology may be a Global System for Mobile communication (GSM) technology, the 3G communication technology may be an Enhanced Data rates for GSM Environment (EDGE) and High Speed Packet Access (HSPA) communication technology, and the 4G communication technology may be a Long-Term Evolution (LTE) communication technology.
As the wireless communication technologies have evolved from the 2G communication technology into the 4G communication technology through the 3G communication technology, their communication conditions, such as modulation resolutions used during A/D modulation, and BandWidths (BW), have been changed as well.
Therefore, complex wireless communication environments have become commonplace, in which different wireless communication technologies or different wireless communication protocols, such as 2G and 3G communication technologies or 3G and 4G communication technologies, coexist. Because of this, terminals supporting wireless communications are developed to have a structure capable of supporting a plurality of different wireless communication technologies.
The 4G wireless communication technology uses the increasing A/D modulation resolution and bandwidth, along its evolution. Therefore, the evolved wireless communication technologies use a structure with a third order or more, capable of implementing high resolution during A/D modulation. However, a structure of an A/D modulation apparatus having a modulation order of a third order or more may have significantly low stability.
For example, in the case of a root-locus for a noise transfer function in each order, in modulation orders of first and second orders, signals converge in an inner area of a unit circuit, which is a stable area. However, in third and fourth orders, which are modulation orders higher than the first and second orders, signals may oscillate without converging in an outer area of the unit circuit, which is an unstable area.
Therefore, although a structure of an A/D modulation apparatus having a second order or less is always stable in system efficiency, a structure of an A/D modulation apparatus having modulation orders of third and fourth orders may be unstable due to amplitudes, frequencies and offsets of signals. These factors may cause a significant decrease in the system efficiency and yield because they vary depending even on temperature and process conditions. To address these problems, A/D modulation apparatuses may have a limiter that prevents oscillations, which, however, makes their design very difficult, and may not fully guarantee stability thereof.
For these reasons, there is a need for an A/D modulation apparatus that may ensure the future stability and a decrease in power consumption, and may meet the A/D modulation resolution required for each communication mode and/or wireless communication protocol to be used.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.